Sullivan recorded two tackles (one solo), two pass breakups and one interception in Sunday's loss to the Browns.
Sullivan signed with the Steelers on Tuesday, Chris Adamski of the Pittsburgh Tribune-Review reports.
Sullivan tallied career highs with 60 tackles (45 solo), seven passes defended and one fumble recovery over 17 games during the 2022 regular season.
Sullivan was not listed on the Vikings' injury report Wednesday.
Sullivan was limited during Wednesday's practice due to an undisclosed injury, Mike Kaye of The Charlotte Observer reports.
Sullivan suffered a knee injury Sunday in the Packers' loss to the Lions on Sunday.
Sullivan made four solo stops and recorded his first interception of the season in Sunday's 24-10 victory over Washington.
Sullivan signed an RFA tender with the Packers on Tuesday, meaning he'll remain with the team next season, Rob Demovsky of ESPN.com reports.
Sullivan (hip) is questionable to return to Sunday's game against the Lions.
Sullivan exited the team's Week 4 contest against Atlanta to be evaluated for a concussion, Olivia Reiner of the Milwaukee Journal Sentinel reports.